Method for extracting water from a paper web in a papermaking machine using a ceramic foam member

ABSTRACT

The invention is directed to a method for extracting water from a paper web in a paper making machine using a ceramic foam component. The component includes a supporting structure and a water permeable member is mounted on the supporting structure and is adapted to support a paper web. The water permeable member comprises a rigid mass of ceramic foam having a plurality of interconnected cells. The ceramic foam has an air permeability in the range of 10 to 1,000 cubic feet per square foot of surface area per minute and has a density of 5 to 100 lbs/cubic foot. When a pressure differential is applied to the permeable member to the paper web, moisture will be extracted from the web and passes through the permeable member.

BACKGROUND OF THE INVENTION

In a typical papermaking process, water is extracted from the paper webor mat in a number of different operations. For example, in the formingsection the paper web is conveyed on a forming wire or belt across aseries of spaced transversely extending foil blades. Each foil blade isprovided with a generally sharp edge facing in an upstream direction andas the paper web passes across the foil blade, a partial vacuum iscreated between the web and the upper surface of the blade, which drawswater from the web. The sharpened edge of the next succeeding bladeriding against the lower surface of the wire will scrape and remove themoisture from the wire.

Water is also extracted from the paper web through use of suction orUhle boxes. The typical suction or Uhle box includes a rigid cover whichsupports the wire that carries the paper web, and the cover is providedwith a plurality of perforations or slots. By drawing a vacuum on theinterior of the box, water is drawn from the paper web into the box.

Water extraction can also be achieved by passing the paper web over aperforated roll, while subjecting the web to a pressure differentialcreated by exposing the interior of the roll to a vacuum.

In other papermaking applications, water is extracted from the web bypassing the paper web, while sandwiched between a pair of porous beltsor wires, around a curved shoe. As the paper web confined between thetwin wires passes around the curved surface, a compressive force isexerted along with centrifugal force which tends to drive the wateroutwardly from the web.

In a dryer section of a typical papermaking machine, the paper web ispassed over a series of heated dryer rolls to drive off the moisture,and in some applications, the dryer rolls may be perforated and apressure differential applied to pass air through the web to facilitatethe drying operation.

The water extracting media, such as suction and Uhle box covers,perforated drums, and the like are generally composed of rigid plastic,metal, or solid ceramic and slots, holes or grooves are machined in thematerial. With this type of construction, the holes or slots arerelatively large in size and when the material in use is subjected to apressure differential, the fiber material of the paper web can be drawninto the holes or slots, causing fiber misorientation in the web. Afurther disadvantage is that the relatively large sized openings, i.e.holes and/or slots, tend to shadow mark the web, which would make thepaper unsuitable for certain applications. Moreover, in the conventionalwater extraction operation, the pressure differential is applied onlythrough the openings and consequently, the water drainage at anyparticular instant is through isolated areas of the web, which resultsin non-uniform water extraction.

SUMMARY OF THE INVENTION

The invention is directed to a method and apparatus for extractingmoisture from a wet paper web in a papermaking machine. The apparatusincludes a supporting structure and a water permeable member is mountedon the supporting structure and a paper web, supported on a movingporous belt, passes over the water permeable member. A pressuredifferential can be applied to the web as it travels over the waterpermeable member to aid in extracting water from the web, and theextracted water drains through the water permeable member.

The water permeable member is composed of a rigid mass of porous ceramicfoam material containing a plurality of interconnected cells. Theceramic foam material has an air permeability in the range of 10 to 1000cubic feet per square foot of surface area per minute, a compressivestrength greater than 100 psi, and a density in the range of 5 to 150lbs/cu.ft.

The permeable member is fabricated by initially producing a polymericfoam element having the same configuration as the permeable member. Thepolymeric foam can take the form of open cell polyurethane foam.

The polyurethane foam substrate is then coated with a liquid slurry of aceramic material, and after draining the excess ceramic material fromthe substrate, the substrate is subjected to an elevated temperature,sufficiently high to burn off the polymeric material and at the sametime fire the ceramic material, thereby resulting in a fired ceramicstructure composed of a lattice-work of interconnected cells. Theresulting ceramic foam material has a predictable porosity, similar tothat of the polyurethane substrate.

The ceramic foam member has a relatively fine uniform porositythroughout its entire surface area, thereby eliminating the possibilityof forming shadow marks on the paper web, as can occur when water isextracted from the web through larger-sized holes or slots.

With the fine porous structure, larger particles and fibers cannotpenetrate the pores, so that the machine will run cleaner andmaintenance will be reduced. Moreover, due to the fine porous structure,there will be a lesser tendency to draw fibers into the pores, thusminimizing fiber disorientation in the paper web.

The ceramic foam member has a high compressive strength and thus can befabricated into articles, such as roll shells and shoes, which aresubjected to a high compressive stress during the papermaking operation.As the ceramic material has high temperature resistance, the ceramicfoam can be fabricated into dryer drum shells, which may be exposed toelevated temperatures during operation.

Since the ceramic foam material has a substantially lesser weight thanmetal, the supporting structures for the ceramic foam material can bereduced in size and when used as a roll shell, a lesser driving force isrequired for rotation of the shell due to the reduction in weight.

The ceramic foam material is also resistant to chemicals, so that thereis virtually no possibility of deterioration of the ceramic foam memberthrough exposure to the papermaking chemicals.

Other objects and advantages will appear in the course of the followingdescription.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention is directed to an article to be used in a water extractingapplication in the forming section, press section or dryer section of apapermaking machine. As an example, in the forming section of a typicalpapermaking machine a cellulosic slurry is contained within a headboxand is discharged from the box onto an endless moving forming wire orbelt in the form of a mat or web. Located immediately downstream fromthe headbox is a forming board which extends transversely across thewidth of the machine. In addition, a series of spaced foil blades arepositioned downstream of the forming board and the foil blades arefollowed by a group of suction boxes. As the paper web is conveyed overthe foil blades and suction boxes by the forming wire, water isextracted from the web in a conventional manner.

In the typical installation, the foil blades each include a generallysharp edge which faces in an upstream direction and rides against thelower surface of the forming wire. As the wire carrying the paper webpasses over the upper surface of the foil blade, a partial vacuum iscreated between the paper web and the foil blade, which acts to drawwater downwardly from the web, and a portion of the water tends tocollect on the undersurface of the wire. The sharpened edge of the nextsucceeding foil blade will ride against the undersurface of the wire tostrip the moisture from the wire.

The typical suction box includes an open-top housing and a perforated orwater permeable cover which supports the moving forming wire and paperweb. The interior of the suction box is connected to a source ofsubatmospheric pressure or vacuum and the vacuum drawn through the coveracts to draw water from the paper web.

In accordance with the invention, a porous ceramic foam material is usedto construct the permeable water extracting members in the papermakingmachine, such as vacuum box covers, and can also be used to producenormally non-porous members, such as foils and forming boards. Byconstructing the forming board and foils of the porous ceramic foammaterial, additional water extraction can be achieved.

In addition, the porous ceramic foam material can be employed inproducing shoes, cylindrical press roll shells, cylindrical dryer rollshells, Uhle box covers, and other water extracting components used in apapermaking machine.

The ceramic foam material is a rigid open cell type that has an airpermeability of 10 to 1,000 cubic feet per square foot of surface areaper minute, a density in the range of 5 to 150 lbs/cubic foot. and acompressive strength in excess of 100 psi. The ceramic foam material hasa bulk density in the range of 10 to 50% of the theoretical density ofthe ceramic.

The ceramic foam is a complex pattern of dodecahedra, which is repeatedin three dimensions. The dodecahedra are defined by ceramic filamentswhich outline the edges of the pores or cells.

The ceramic foam article is constructed by initially producing asubstrate of polymeric foam that is identical in configuration to theceramic foam article to be subsequently produced. The polymeric foam ispreferably polyurethane foam and is an open cell type being composed ofa plurality of interconnected cells. After the polymeric foam is formedinto the desired shape, it is impregnated with a liquid ceramic slurry,preferably an aqueous slurry. The ceramic material can take the form ofsintered aluminum oxide, magnesium oxide, zirconium oxide,zirconium/aluminum oxide, chromium/aluminum oxide, mullite, cordierite,silicon carbide, or the like.

After the entire internal cell structure of the polymeric foam has beencoated with the ceramic slurry, the excess slurry is removed as bysqueezing, thereby leaving a ceramic coating on all of the internal andexternal surfaces of the foam.

The coated foam substrate is then subjected to an elevated firingtemperature above the temperature to decompose the polymeric foam andsufficient to fire the ceramic material. In general, the firingtemperature will be in the range of 1000° F. to 4000° F., with thespecific temperature depending upon the ceramic material being used.After firing, a rigid porous mass of ceramic material is produced havinga lattice-work of interconnected cells with a porosity similar to thatof the original polymeric foam material.

In operation, the wet paper web is carried through the sections of atypical papermaking machine succesively by a forming wire, apapermaker's felt, and a dryer felt. As the paper web, carried by thewire or felt, passes over the water extracting component formed of foamceramic material, a pressure differential can be applied to the web,causing water to be extracted from the web and the water drains throughthe porous ceramic foam material.

As the ceramic foam material has a fine porous structure, harshpull-down of the fibers into the water drainage openings, as occurs inconventional papermaking machines, is eliminated. As an additionaladvantage, larger particles and fibers cannot penetrate the fine porousstructure, so that the machine runs cleaner and requires lessmaintenance.

As the ceramic foam material has a high compressive strength it can beused to produce articles or components which are subjected in use torelatively high compressive stress, such as press roll shells, dryerroll shells and shoes.

Moreover, the fine porous structure eliminates the possibility of shadowmarking on the paper web, as can occur with a conventional waterextraction medium having larger sized holes or slots.

Further, because of the more effective dewatering achieved by the mediumof the invention, the overall size of the papermaking machine isreduced.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

I claim:
 1. A method of extracting water from a paper web in apapermaking machine, comprising the steps of forming an article of anopen cell polymeric foam material, coating the internal and externalsurfaces of said polymeric foam material with a liquid slurry of aceramic material to form a coated article, heating the coated article toan elevated temperature sufficiently high to decompose said polymericmaterial and to fire said ceramic material to thereby produce a rigidporous mass of foam ceramic material having a plurality ofinterconnected cells, passing a wet paper web in contact with saidporous ceramic foam mass, and draining water from said web through saidmass as said web passes in contact with said mass.
 2. The method ofclaim 1, wherein the coated article is heated to a temperature of 1000°F. to 4000° F.
 3. The method of claim 1, wherein said open cellpolymeric foam material is polyurethane foam.
 4. The method of claim 1,wherein said liquid slurry is an aqueous slurry.
 5. The method of claim1, wherein the ceramic material is selected from the group consisting ofsintered aluminum oxide, magnesium oxide, zirconium oxide,zirconium/aluminum oxide, chromium/aluminum oxide, mullite, cordierite,silicon carbide, and mixtures thereof.
 6. A method of extracting waterfrom a paper web in a papermaking machine, comprising the steps offorming an article of an open cell polymeric foam material, coating theinternal and external surfaces of said polymeric foam material with aliquid slurry of a ceramic material to form a coated article, heatingthe coated article to an elevated temperature sufficiently high todecompose said polymeric material and to fire said ceramic material tothereby produce a rigid porous mass of foam ceramic material having aplurality of interconnected cells, supporting a wet paper web on aporous moving member, passing said porous member and the supported webover a surface of said porous ceramic foam mass, applying a pressuredifferential to opposite surfaces of said web as said web passes oversaid mass to extract water from said web, and draining the extractedwater through said mass.
 7. The method of claim 6, wherein said step ofapplying a pressure differential comprises applying a vacuum throughsaid ceramic mass to said web.